In favour of saints supporting church operation (7)
I believe the answer is:
process
'operation' is the definition.
(thesaurus)
'in favour of saints supporting church' is the wordplay.
'in favour of' becomes 'pro' (I've seen this before).
'saints' becomes 'ss'.
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'church' becomes 'ce' (abbreviation for Church of England).
'ss' after 'ce' is 'cess'.
'pro'+'cess'='PROCESS'
(Other definitions for process that I've seen before include "Series of actions to achieve a result" , "Use IT perhaps < to handle" , "Deal with, action" , "Natural series of changes" , "that's the course of action" .)